Process for purifying impure lead



Patented Mar. 8, 1938 PATENT GFFKIE PROCESS FOR PUBIFYING IMPURE LEADFerdinand Leferrer, Paris, France, assignorto Societe Miniere etMetallurgiqne de Penarroya, Paris, France, a corporation of France NoDrawing. Application October 25, 1935, Se-

rial No. 46,826. In France November 2, 1934 g 1 Claims. It is well knownthat most of the molten alloys give when slowly cooled a series of solidproducts the composition of which varies in a continuous manner from thebeginning to the end of the solidification.

Only eutectic. alloys do not follow this rule.

It is thus often possible to modify the composition ofan alloy and toobtain a more or less complete separation of its constituents through apartial solidification with 'a separation of the solid and liquid phaseswhich are in presence, in well determined conditions.

This property has been used for a long time in metallurgical processesfor the refining of metals.

It has already been proposed to amplify this phenomenon and to rendermore eflicient the separation of the constituents by adding to themolten alloy, prior to the partial solidification. certain elementsconveniently selected.

Thus, by adding a suiiicient quantity of zinc to molten argentiferouslead it has been possible to obtain, by cooling in the neighbourhood ofthe temperature of solidification of the lead, a floating solid crustwhich it is easy to separate and which carries with itselfthe totalityof the silver pre-existing in the lead. I

More recently it has been tried, by using additions of alkaline orearth-alkaline metals, to

separate thelead from its alloys and especially from copper, tin,antimony, arsenic and bismuth with which it was possibly alloyed.

i It has therefore been indicated that only additions of earth-alkalinemetals (calcium, magnesium or barium) made it possible to eliminate thecopper, whileit was preferable to use additions of sodium for separatingarsenic, antimony and bismuth.

But the experiments which have been made in this way have notalwaysgiven-the anticipated results. It has been found that sodiumhad'no action on bismuth which could be separated-only through theearth-alkaline metals (which has precisely given rise to a commercialprocess for debismuthizing lead).

Lastly, antimony couldbe separated from lead by means of sodium only inalloys having a large content of antimony.

Then it has been found, according to this invention, that additions ofsodium alone to impure leads in a molten condition,--containing no oronly a very small proportion of zinc, but containing copper, with as thecase may be, tin

and/or arsenic, and/or antimony and/or precious,

metals-'-, made it possible to separate by cooling and in thesame'fioating crust almost the totality of the copper and as the casemay be, of the tin, of the arsenic, and also eventually part of theantimony (according to the proportion of sodium used); precious metals,if any, being not eliminated.

Thus, if a liquid working lead known as lead base bullion (having beenfreed from inclusions of matts and slags by melting and skimming at alow temperature) is treated through metallic sodium, the arsenic and thecopper and the tin will be eliminated in the form of a crust which willfloat on the upper sin-face of the bath.

The-antimony will remain in the lead orit will be partly eliminatedaccording to the quantity of sodium which has been added to the,

working lead.

Gold and silver will remain in the lead.

For carrying the process into practice metallic sodium or sodium" alloysmay be used.

The excess of sodium remaining in the lead after treatment can beeliminated by a treat-v composition containing 0.3% of arsenic, 0.08% oftin, 0.3% of antimony, 0.05% of copper and. a

0.1% of silver, metallic sodium in the proportion of 5 kg. of sodium fora ton of lead, there will be obtained, after skimming at a temperatureof about 330 C. (626 F.) a lead containing less than 0.01% of arsenic,less than 0.005% tin and less than 0.005% of copper. s The content ofantimony will remain of about 0.3% and the content of silver will remainof about 0.1%- a By adding to the same molten working lead'a greaterproportion of sodium, for instance 15 kg. of sodium for a ton of lead,the arsenic content of the lead obtained afterskimming will be less than0.005%, thetin less than 0.002%, the copper content will be less than0.002% and the antimonycontentwillbelessthanorequal to 0.1%. The silverwill remain in the lead, with a silver content of about 0.1%.

This process allows also-by adding a quantity of sodium which issufficient for eliminating the impurities but which is not suflicientfor eliminating the antimony"-of purifying any lead-antimony alloy forfreeing it from the impurities which it contains (arsenic, copper forinstance) It has been thus possible, for instance, to purlfy'alead-antimony alloy having the following composition: arsenic 0.1%, tin0.05%, copper 0.05% and antimony 10%, by adding to the same 0.4% ofsodium. After the known treatment,

for instance with water or steam, in order toarsenic, about 0.3%antimony, about 0.05% cop-' per, and about 0.1% silver, adding metallicsodium intheproportionot5kg.ofsodiumpertonoi lead, skimming the dross ata temperature of about 330 C, thereby obtaining a lead containing lessthan 0.01% arsenic, and less than 0.005%

copper, the antimony and silver remaining substantially unchanged.

2. In a process for purifying impure leads and especially work leadscontaining about 0.3% ar-. senlc, about 0.3% antimony, about 0.05%copper, and about 0.1% silver, adding metallic sodium in the proportionof 15 kg. of sodium per ton of lead.

skimming the dross at a temperature of about.

330 0., thereby obtaining a lead havingless than 0.005% arsenic, lessthan 0.002% copper, less than 0.1% antimony, the silverremainingsubstantially unchanged.

3. A process for purifying lead base bullion containing a small amountof tin, from trace to about 1% arsenic, from trace to about 0.15%copper, from trace to about 1% antimony, bismuth and noble metals whichconsists in adding a small amount of sodium to a molten bath of saidbullion, allowing the bath to cool and removing simultaneously in thecrust formed on the upper part of the bath all the copper, tin andarsenic present;

.- the antimony, bismuth and noble metals remaining in the bath. 4. Aprocess for purifying lead base bullio containing a small amount oftin,from trace to I mony, bismuth and noble metals about 1% arsenic, fromtrace to about 0.15% copper, from trace to about 1% antimony,bismuth andnoble metals which consists in adding to a molten bath of said bullionan amount oi sodium greater than that necessary for eliminating arsenic,tin and copper,-allowing the bath to cool and removing simultaneously inthe crust formed on the upper part or the bath all the copper. tinandarsenic, with a part oi the antimonyin relation-to the excess ofsodium added, the bismuth and noble metals and the restoi' antimonyremaining in the bath.

5. The process of purifying a hard lead containing a. small amount oftin, an amount 01 antimony oi the order oil-about 10% and one or more ofthe group comprising arsenic of the order of about 0.1 copper oi theorder 01' about 0.05%,

which consists in to a molten bath 0! said lead a small amount ofsodium, allowing the bath to cool and removing simultaneously in thecrust formed on the bath all the copper, tin and arsenic present, theantimony remaining in-the hath.

. 6. A process for purifying lead base bullion containing the-usualsmall mounts of arsenic, copper, tin, antimony, bismuth and noblemetals. which consists in adding a small amount oi sodium to amolten-bath of said bullion, allowing the bath towel and removingsimultaneously in the crust formed on the upper part of the bath all thecopper, tin andarsenic present; the antiremaining .in the bath.

7. A process for-purifying lead base'bullion containing the usual small.amounts of arsenic,

.copper, tin, antimony, bismuth and noble metals,

.which c'onsists in adding to a molten bath of said bullion an amount orsodium greater than that necessary for eliminating arsenic, tin andcopper,

, allowing the bath. to cool and removing simultaneously in the crustformed on the upper part of the bath an the copper, tin and arsenic,with a part oi the antimony in relation to the excess of sodium added,the bismuth and noble metals and the rest of antimony remaining in thebath.

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